One of the major issues in many Low power and Lossy Networks (LLNs) is link congestion: not only is the bandwidth very limited, but it is well-known that the efficiency of data transmission greatly degrades (e.g., collapses) once the offered load exceeds some known limit. For instance, in shared media networks, such as wireless networks, the higher the traffic through a specific link, the higher is the probability of packet collisions (over that link). As the number of collisions on a specific link increases its effective bandwidth diminishes. Additionally, packet collisions may necessitate packet re-transmission which artificially increases the number of packets the network attempts to transmit over the specific link. The fact that the network attempts to transmit more packets into a diminishing bandwidth may cause a collapse/degradation in network performance over this specific link.
Generally, not all locations in a network suffer from the same congestion problems and often not at the same time. That is, there may be certain locations (nodes/links) referred to as “choke points” within the network where most of the congestion (contention, collisions, interference) occurs. For example, in directed acyclic graphs (DAGs), which are frequently point-to-multipoint (P2MP) or multipoint-to-point (MP2P), choke points may frequently occur at or near a “root” node of the DAG, as well at other locations within the DAG depending upon the specific topology of the DAG.